a) Field of the Invention
The present invention relates to a process for the preparation of .alpha.-tocopherol derivatives (VII) which are useful as antisterile vitamins, hypolipidemics, blood flow increasing agents, oxygen radical scavengers, anti-cytosenility agents, antioxidants and the like.
b) Description of the Related Art
.alpha.-Tocopherol derivatives represented by the following formula (VII): ##STR2## wherein n stands for 0 or an integer of from 1 to 5 have heretofore each been prepared by condensing trimethylhydroquinone represented by the following formula (I): ##STR3## with one of phytols represented by the following formulae: ##STR4## in accordance with a Friedel-Crafts reaction. ##STR5##
The catalyst is essential for the Friedel-Crafts reaction. Described specifically, Lewis acids such as zinc chloride, alumimum chloride, stannic chloride, ferric chloride, titanium tetrachloride and boron trifluoride-ether complex as well as combinations of Lewis acids and protonic acids such as hydrochloric acid, sulfuric acid and phosphoric acid have been used. However, these catalysts employed in the conventional preparation processes of .alpha.-tocopherol derivatives (VII) are accompanied by the problem that they cannot be recovered and reused because they are extremely unstable to water and are decomposed or deactivated upon contact with water formed in the reactions or during washing with water. Further, it is difficult from the standpoint of environmental conservation to dispose zinc, tin, phosphorus and the like. All of the conventional preparation processes are therefore not considered to be industrially suited.
In order to improve the aforementioned drawbacks, the utilization of fixed catalysts has been discussed. For example, Japanese Patent Publication No. 11709/81 discloses a process employing zeolite in which a substitutable group thereof is substituted with a proton, Japanese Patent Publication No.22868/81 discloses a process employing silica-alumina, alumina-boria, zeolite and a fixed acid such as silica-alumina or alumina having zinc sulfate, nickel sulfate, aluminium sulfate or iron sulfate carried thereon, and Japanese Patent Publication No. 45195/85 discloses a process employing a metallic chelate sulfonic acid resins having a Lewis acid activity. Further, it has been known that a cation exchange resin is utilizable as the fixed catalyst.
In the case of the zeolite type catalyst described in Japanese Patent Publication No. 11709/81, such catalyst must be used preferably in an amount of 1.about.50 parts by weight to the feed material "trimethylhydroquinone (I)". This process was not an industrially actual process because the reaction volume is extremely increased. In addition, the obtained .alpha.-tocopherol had a GLC purity as low as 89-94% even when it was distilled under high vacuum, as described in Example.
The fixed acid carried on silica-alumina or alumina, described in Japanese Patent Publication No. 22868/81, involved problems, i.e. a larger amount of its use to the feed material and a yield as low as 20.about.65%. In order to improve the yield, furthermore, it was necessary to use an extremely toxic halogenated hydrocarbon such as perchloroethylene (tetrachloroethylene).
In the case of the metallic chelate sulfonic acid resin having a Lewis acid activity, described in Japanese Patent Publication No. 45195/85, the yield was 80-90% and this was not sufficient from the industrial standpoint.
Further, in the case of the cation exchange resin, it was not practical because of a very lower yield of 10%, as described in Comparative Example of Japanese Patent Publication No. 22868/81.
The conventional fixed catalysts employed in the preparation of the .alpha.-tocopherol derivatives (VII) involve many problems, for instance a lower yield and a need of a highly toxic solvent, as described above. It has therefore been desired to develop an industrially excellent fixed catalyst as a substitute for such conventional catalyst.